1. Field of the Invention
The present invention relates to an optical information recording medium, more specifically, to an optical information recording medium such as a CD-R (compact disk recordable) medium, and a CD-RW (compact disk rewritable) medium, and particularly, to an optical information recording medium having a ROM area in which pre-pits are arranged in advance and a recordable area in which a guiding groove is arranged.
2. Discussion of the Background
A recordable compact disk (CD) called “CD-R” is prescribed in the Orange Book, an industry standard. An ordinary CD-R has a pre-groove arranged on its entire surface. The pre-groove wobbles, and by changes of the wobbling period, time information called “ATIP” (absolute time in pre-groove) is recorded. A CD-R is partitioned, from the central part outward, into the following areas: a PCA (power calibration area) in which the light level is set, a PMA (program memory area) in which recording location information is recorded, an LIA (lead-in area) in which contents information (table of contents) is recorded, and an information area (program area) in which data is recorded. Information is recorded by recording pits along the pre-groove using a CD writer.
A CD-R can be written-once by recording the recorded location information (ATIP time) into PMA after recording information. Thus, after writing once into CD-R, pits are formed in a part of the information area and a part of PMA. Also, there is a CD-R, on which pre-pits are partly recorded in advance, called a “hybrid disk”. Part of the information area and PMA are formed by pre-pits. The pre-pits wobble in the same manner as a pre-groove.
FIGS. 8A–8D and 9A–9E illustrate an example method for creating a hybrid CD-R. In a resist-forming process as shown in FIG. 8A, a disc-shape glass plate 10 is prepared, with two layers of photo resist 11 and 13 formed sandwiching an interlayer 12. In an exposure process as shown in FIG. 8B, a laser beam L is irradiated onto the photo resist films 11 and 13 by an exposure apparatus while rotating the films, thereby forming a spiral-shaped latent image i on the photo resist films 11 and 13. Then, in a development process as shown in FIG. 8C, the latent image portion is dissolved. At this time, a deep pre-pit 1 and a sallow groove (groove between the pre-pits) 2, which are created distinctively by controlling the light level of the exposure during the above-mentioned exposure time, are obtained. In this regard, in FIG. 8C, I1, I2, and I denote the recording area, the ROM area, and the information area, respectively.
Then, in an electroforming process as shown in FIG. 8D, an electroforming layer which will be used as a stamper 14 is formed, in a glass-detachment process as shown in FIG. 9A, a glass plate is detached, and then in a resist-removing/stamper-forming processes as shown in FIG. 9B, the remaining photo resist 11 and 13 are removed to form a stamper 14 which includes a deep pit-formed part 1′ having a depth from the top surface of the photo resist 13 to the bottom of the lower photo resist 11 and a shallow groove formed part 2′ having a depth from the top surface of the photo resist 13 to the top surface of the lower photo resist 11.
In a formation process as shown in FIG. 9C, formation is performed using the obtained stamper 14, and a large number of formation plates 15 are replicated. Then, in the process of applying recording agent as shown in FIG. 9D, recording agent 16 is applied to the entire surface of the formation plate 15, and furthermore, a reflection layer 17 and a protection layer 18 are formed during the formation process of the reflection layer/protection layer as shown in FIG. 9E. Through the above processes, a hybrid CD-R on which information is recorded partly in advance by an exposure apparatus is created.
Next, a conventional example will be specifically described. Conventionally, there has been a problem in that a tracking error signal (push-pull signal) of a ROM (Read Only Memory) area, which is formed by pre-pits, is smaller than that of a recodable area which is formed by a pre-groove. In order to improve this, for example, in Japanese Laid-Open Patent Publication No. 5-6578, the tracking error in the pre-pit area has been improved by forming a groove between the pits which is wider and shallower than a pre-groove between address pits of an information recording medium.
Also, in Japanese Laid-Open Patent Publication No. 5-12680, a pre-groove between the pits, which has the same depth and width as a pre-groove between the pre-pits of the above-described hybrid disk, is formed, thereby eliminating fluctuations of reflection rate in the pre-pit area and pre-groove area. In addition, in Japanese Laid-Open Patent Publication No. 6-131701, a groove between pits is formed between pre-pits such that the tracking error signal becomes the same in the recordable/reproducible area in which pre-groove is formed as in the reproduction-only area in which pre-pits are formed in a partial ROM where both the recordable/reproducible area and the reproduction-only area exist.
In addition, in Japanese Laid-Open Patent Publication No. 8-7339, in a partial ROM, in order to improve the tracking error signal and CTS (cross track signal) in the reproduction-only area in which pre-pits are formed, a groove between the pits which is narrower than the pre-pits and shallower than λ/8n is formed between the pre-pits. Also, as described in Japanese Laid-Open Patent Publication No. 5-36087, there arises a problem that when a pre-pit has wobbling, the WCN (wobble C/N ratio) becomes lower as compared to that with a pre-groove, and jitter increases as the wobbling amount increases. As a means to solve this, a groove is formed between the above-described pre-pits.
FIGS. 10A–10B and 11A–11B illustrate a groove between the pits which connects pre-pits as described above. FIG. 10B shows schematically a sectional view (a cross-sectional view of CD-R in a circumferencial direction) of FIG. 10A. Also, FIG. 11A shows schematically a partially-enlarged plan view of a conventional pit structure having a groove between pits. FIG. 11B shows schematically a sectional view (a cross-sectional view of a CD-R in a circumferencial direction) of FIG. 11A. Also, FIG. 12 is a partial perspective view of a ROM area in which pre-pits 1 and grooves between the pits 2 are formed as shown in FIGS. 11A and 11B.
As shown in FIGS. 11A and 11B, there has been a problem in that when connecting one pre-pit 1 with another by a groove 2 between pits, as a result of the influence of the groove between the pits, the pre-pit 1 is extended in the direction of the track. This extension is not uniform, and the angle of inclination becomes small in cross-section of pre-pits 1 in the direction of track, thereby deteriorating the jitter.
Also, as shown in FIGS. 13A and 13B, when pre-pits wobble, the WCN (Wobble C/N ratio) is lower than that with a pre-groove, thus as the amount of wobbling increases, the jitter increases. To solve this, the above-described groove between the pre-pits is an effective method.